This invention relates to dot matrix type serial printing devices and more particularly to the means for controlling transverse feed and printing operation of the printing head assembly thereof.
Generally, in a serial printing device of the dot matrix type, the printing head assembly includes a set of printing elements in the form of print wires arranged in vertically aligned relation which each other and electromagnetic actuator means provided for driving the respective printing elements. In operation of the printer, the printing elements are selectively driven by the actuator means to print a dot or dots on the surface of a paper document or other printing surface each time the printing head assembly is fed transversely a pitch distance. A plurality of the dot columns consecutively printed on the printing surface are related so as to form any desired character or symbol within a definite size of dot matrix.
Heretofore, in a serial printing device of the type described, an AC motor has ordinarily been employed as a source of power for feeding the printing head assembly transversely thereof with two clutch mechanisms associated with the AC motor for selection of the direction of movement of the printing head assembly for printing operation and restoration thereof to the rest position. The printer has also included a stationary strap member which extends in the direction of movement of the printing head assembly and is formed therein with a row of slits corresponding to respective printing positions of the printing head assembly; and, in order to detect such slits in the strap member, a photoelectric sensing unit has been mounted on the carriage of the printing head assembly. Serial printers of such known form, however, have involved various deficiencies as described below.
First, in the form of printer, the power transmission system between the power source and the printing head carriage has unavoidably been complicated, including mechanisms provided independently from each other for transverse feed control of the carriage and for controlling the print wire actuator means of the printing head assembly. Under the circumstances, the printer has included a large number of component parts, necessitating a high cost of fabrication and a large space for installation.
Further, with the previous form of serial printer, the AC motor and part of the power transmission system have been kept running even when the printer is idle or in a standby condition, thus causing a definite loss of electric power and considerable noise.
In addition, in the previous printer, since the transverse feed of the printing head assembly and the dot printing operation thereof are controlled independently from each other, as described hereinbefore, by the respective control mechanisms, any variation in rate of transverse feed of the printing head assembly has been liable to result in driving the print wires at time intervals shorter than the minimum period allowable for the print wires to properly respond to the electromagnetic drive of the wire actuator means. In such a situation, there has always been the danger that one or more of the dots required to form a character be missed, thus rendering the character formed imperfect and hardly legible.